Long before 3GPP had sang standard for transporting A over IP, some companies implemented what is called SCCPLite. This uses the IPA multiplex over TCP as transport for SCCP, together with MGCP for configuring RTP media flow IP/Port information.

Osmocom implements this so far only in osmo-bsc-sccplite and osmo-bsc_nat.

Later, 3GPP standardized a method on how to transport A interfaces over IP and called it AoIP. It uses real SCCP over M3UA/SCTP/IP for the signalling plane and replaces the G.711 TDM user plane with using untranscoded air interface codec payload in RTP/UDP/IP. See 3GPP TS 48.103 for the user plane (RTP) handling.

The BSSMAP protocol was extended to be able to negotiate per-call IP/Port information between BSC and MSC.

Osmocom OsmoBSC works with 3GPP AoIP and has been tested to interoperate with several MSCs, not just OsmoMSC